Glossary of Video Quality Terminology

Common terms you need to know to compare and evaluate the quality and broadcast format of digital videos.

The Basics

DTV – Digital Television – A broad term that simply means the television broadcast signal is being transmitted in a digital format. “DTV” does not include a definition of which resolutions are used.

Field – Refers to the set of odd or even scanlines (horizontal lines) of a video in interlaced video. Interlaced video displays odd scanlines first, followed by even scanlines. The number of times these fields are changed is referred to as fieldrate, and is generally twice the framerate.

FrameA frame is one still picture of a video. By displaying these still pictures, frames, rapidly in sequence, the human eye loses track of individual frames and perceives the images as in motion.

HD – High Definition – Refers to the resolution of digital video. 1280×720 and 1920×1080 are the most common resolutions referred to as High Definition.

HDTV High Definition Television – Is a format standard that specifies an aspect ratio of  true 16:9 and one of the following HDTV resolutions: 1080i or 720p. Not to be confused with DTV that does not specify format or aspect ratios, or simply HD that isn’t television explicit.

Interlaced – Interlacing is a method of smoothing video picture. This is done by splitting each frame across two fields by alternating horizontal lines (12121212, con’t). Contiguous frames are served in a rolling sequence:

Interlacing creates a visual trick that makes the fps appear to be double what it really is – this is sometimes referred to as fieldrate, or described in terms of Hz frequency. All analog video is interlaced frame type.

Progressive – Progressive video displays frames, in whole, one after each other, unlike interlaced formats where the frames are split into fields and contiguous images are overlapped on a frame (essentially doubling the number of images per second). In a progressive frame type, framerate is the same as image rate.

SDStandard Definition – SD refers to video encoded for use with legacy analog TV systems.

SDTV – SDTV is the digital TV standard with a resolution of 720×480. SDTV formats include 480i & 480p.

Evaluating Quality

Resolution – Resolution describes the number of pixels shown on a computer or TV screen. It is expressed as the number of horizontal pixels by the number of vertical pixels: 720 (horizontal pixels) x (by) 480 (vertical pixels). The higher your resolution, the more detailed your images can be.

When referring to digital video, the amount of detail stored in the video source is called the Display Resolution and is expressed in the same way. Also in the same way, the higher your resolution, the sharper and larger your video will be.

In broadcast television, the video format will include information about the resolution of your video. 720p, for example, refers to video that is encoded with 720 horizontal lines at an aspect ratio of 16:9 to generate a resolution of 1280×720.

Aspect Ratio  - Aspect Ratio (AR), most simply, is a term that refers to the comparison of an image’s width to its height. A standard, analog TV has an aspect ratio of 4:3, which means that for every four units of width, it is 3 units high. Widescreen aspect ratio is generally 16:9.

In broadcast television, the video format will include information about the aspect ratio of your video. 720p, for example, refers to video that is encoded with 720 horizontal lines at an aspect ratio of 16:9.

Framerate, fps – Framerate describes how many still pictures (frames) are shown in a unit of time, usually seconds or fps. The human eye will cease to perceive individual frames and view images as in motion when framerate is greater than 24 fps.

The American TV standard, NTSC, framerate is approx. 29.97 fps. The European PAL system framerate is 25fps.

Broadcast Standards

Set of specifications that includes resolution, aspect ratio, display type (interlaced or progressive) and sometimes framerate.

1080i – The broadcast standard that refers to an interlaced HDTV signal with 1080 horizontal lines, an aspect ratio of 16:9 and a resolution of 1920×1080. Offers the highest standard available for TV signals.

1080p – The broadcast standard that refers a progressive HDTV signal with 1080 horizontal lines, and aspect ratio of 16:9, and a resolution of 1920×1080. Currently, 1080p is not available in broadcast HDTV standards and only Blue-ray and HD DVD use 1080p.

480i – The broadcast standard that refers to interlaced video encoded with 240 line fields and a frame of 480 pixels tall. 480i is most suited to TV content that is filmed or edited on analog tape sources like videotape or home videos. Framerate is generally 29.97 fps.

480p – The broadcast standard that refers to a progressive video encoded in frames 480 pixels tall. Often used for video from film sources.

720p – The broadcast standard that refers to a progressive HDTV signal with 720 lines, an aspect ratio of 16:9 and a resolution of 1280×720. Sports broadcasts are generally produced in this format.

NTSC – National Television System Committee -  NTSC is the analog TV standard specifying 486 horizontal lines and a framerate of 29.97 fps. The term can also be used to describe any video, including digital video, that is formatted for delivery to a NTSC television.

PAL – Phase Alternating Line – PAL is the analog TV standard used in most of the western European countries, Australia, and some others. PAL specifies 576 horizontal lines and a framerate of 25 fps.

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